Modulating thickness of colored fluid in color display

ABSTRACT

An embodiment is a display unit. The display unit includes a substrate layer, a layer of colored fluid on the substrate layer, and a transparent actuator element on the layer of the colored fluid. The layer of colored fluid has a thickness and a color. The transparent actuator element modulates the thickness of the colored fluid upon activated by a force such that the colored fluid is changed from a first state to a second state or vice versa. The modulated thickness provides a variable optical density of the colored fluid.

CROSS-REFERENCE TO RELATED APPLICATIONS

The current application is a divisional application of U.S. patentapplication Ser. No. 12/240,810 (20071062-US-NP), filed on Sep. 29,2008, and now patented as U.S. Pat. No. ______, which application isspecifically incorporated herein, in its entirety, by reference.

BACKGROUND

1. Technical Field

The presently disclosed embodiments are directed to the field of displaytechnology, and more specifically, to color display.

2. Background

Display technologies have been developed to provide displays used in awide range of applications from hand-held devices to flat-paneltelevision set. Conventional color displays usually employ a displaymedium which changes in brightness and color filters on adjacent pixels,typically red, green, and blue (RGB) filters. In reflective displays thecolor saturation and the white/black states are not very good when usingthis method. Ideally, color is generated similar to printing orphotography by overlaying cyan/magenta/yellow filter layers. However,this is difficult to achieve in an electronic display which requireschanging the state, i.e., color, of the display.

Existing techniques to provide reflective displays have a number ofdrawbacks. The liquid crystal based techniques may have lowreflectivity, poor contrast ratios, and poor color saturation. Themicro-electromechanical approaches may also have limited reflectivityand poor color saturation. In addition, approaches that employ stackeddisplay panels of different colors such as stacked cholesteric liquidcrystal displays may be complex to fabricate and expensive.

SUMMARY

One disclosed feature of the embodiments is a display unit. The displayunit includes a substrate layer, a layer of colored fluid on thesubstrate layer, and a transparent actuator element on the layer of thecolored fluid. The layer of colored fluid has a thickness and a color.The transparent actuator element modulates the thickness of the coloredfluid upon activated by a force such that the colored fluid is changedfrom a first state to a second state, or vice versa. The modulatedthickness provides a variable optical density of the colored fluid.

One disclosed feature of the embodiments is a method for color display.A plurality of layers of colored fluid is stacked on each other. Each ofthe colored fluid has a color and a thickness and is on a substratelayer. A force is activated on a transparent actuator element on each ofthe layers of the colored fluid to modulate the thickness such that thecolored fluid is changed from a first state to a second state or viceversa. The modulated thickness provides a variable optical density ofthe colored fluid layer.

One disclosed feature of the embodiments is a method to construct acolor display unit. A layer of colored fluid is deposited on a substratelayer. The layer of colored fluid has a thickness and a color. Atransparent actuator element is formed on the layer of the coloredfluid. An actuation mechanism is formed to create a force causingmovement of the transparent actuator element when activated, themovement of the transparent actuator element modulating the thickness ofthe layer of colored fluid such that the colored fluid is changed from afirst state to a second state or vice versa. The modulated thicknessprovides a variable optical density of the colored fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments may best be understood by referring to the followingdescription and accompanying drawings that are used to illustrateembodiments. In the drawings:

FIG. 1 is a diagram illustrating a display unit in which one embodimentmay be practiced.

FIG. 2A is a diagram illustrating a component color block at a firststate according to one embodiment.

FIG. 2B is a diagram illustrating a component color block at a secondstate according to one embodiment.

FIG. 2C is a diagram illustrating a component color block at a thirdstate according to one embodiment.

FIG. 3 is a diagram illustrating a component color block inthree-dimensional space according to one embodiment.

FIG. 4A is a diagram illustrating the top view of a square pattern ofthe adjacent color blocks according to one embodiment.

FIG. 4B is a diagram illustrating the top view of a rectangular patternof the adjacent color blocks according to one embodiment.

FIG. 4C is a diagram illustrating the top view of a hexagonal pattern ofthe adjacent color blocks according to one embodiment.

FIG. 4D is a diagram illustrating the top view of a triangular patternof the adjacent color blocks according to one embodiment.

FIG. 5A is a diagram illustrating a component color block using astructure in a first state according to one embodiment.

FIG. 5B is a diagram illustrating a component color block using astructure in a second state according to one embodiment.

FIG. 6A is a diagram illustrating a component color block using aperforated actuator element in a first state according to oneembodiment.

FIG. 6B is a diagram illustrating top view of the component color blockusing a perforated actuator element in a first state according to oneembodiment.

FIG. 6C is a diagram illustrating a component color block using aperforated actuator element in a second state according to oneembodiment.

FIG. 6D is a diagram illustrating top view of the component color blockusing a perforated actuator element in a second state according to oneembodiment,

FIG. 7A is a diagram illustrating a component color block using abimorph actuator in a first state according to one embodiment.

FIG. 7B is a diagram illustrating a component color block using abimorph actuator in a second state according to one embodiment.

FIG. 8A is a diagram illustrating a component color block using anotheractuation mode in a first state to move the colored fluid from asubstantially vertical into a substantially horizontal or planarposition according to one embodiment.

FIG. 8B is a diagram illustrating a component color block using anotheractuation mode in a second state to move the colored fluid from asubstantially vertical into a substantially horizontal or planarposition according to one embodiment.

FIG. 9A is a diagram illustrating a component color block using anelectrostatic force in a first state according to one embodiment.

FIG. 9B is a diagram illustrating a component color block using anelectrostatic force in a second state according to one embodiment.

FIG. 10A is a diagram illustrating a component color block using anelectro-active polymer (EAP) in a first state according to oneembodiment.

FIG. 10B is a diagram illustrating a component color block using anelectro-active polymer (EAP) in a second state according to oneembodiment.

FIG. 11A is a diagram illustrating a component color block using a shapememory actuator in a first state according to one embodiment.

FIG. 11B is a diagram illustrating a component color block using a shapememory actuator in a second state according to one embodiment.

FIG. 12A is a diagram illustrating a top view of a shape memory actuatoraccording to one embodiment.

FIG. 12B is a diagram illustrating a side view of a shape memoryactuator according to one embodiment.

FIG. 13A is a diagram illustrating a component color block using abi-stable display operation in a first state according to oneembodiment.

FIG. 13B is a diagram illustrating a component color block using abi-stable display operation in a second state according to oneembodiment.

FIG. 14A is a diagram illustrating a component color block using anelectroactive polymer in a first state according to one embodiment.

FIG. 14B is a diagram illustrating a component color block using anelectroactive polymer in a second state according to one embodiment.

FIG. 15 is a diagram illustrating a pixel addressing using localizedcharges according to one embodiment.

FIG. 15A is a diagram illustrating localized charges according to oneembodiment.

FIG. 16 is a flowchart illustrating a process to construct a displayunit according to one embodiment.

FIG. 17 is a flowchart illustrating a process to form an actuatorelement according to one embodiment.

FIG. 18 is a flowchart illustrating a process to form an actuationmechanism according to one embodiment.

DETAILED DESCRIPTION

One disclosed feature of the embodiments is a display unit. The displayunit includes a substrate layer, a layer of colored fluid in a color onthe substrate layer, and a transparent actuator element on the layer ofthe colored fluid. The layer of colored fluid has a thickness and acolor. The transparent actuator element modulates the thickness of thecolored fluid upon activated by a force such that the colored fluid ischanged from a first state to a second state or vice versa. Themodulated thickness provides a variable optical density of the coloredfluid layer.

In the following description, numerous specific details are set forth.However, it is understood that embodiments of the invention may bepracticed without these specific details. In other instances, well-knowncircuits, structures, and techniques have not been shown to avoidobscuring the understanding of this description.

One disclosed feature of the embodiments may be described as a processwhich is usually depicted as a flowchart, a flow diagram, a structurediagram, or a block diagram. Although a flowchart may describe theoperations as a sequential process, many of the operations can beperformed in parallel or concurrently. In addition, the order of theoperations may be re-arranged. A process is terminated when itsoperations are completed. A process may correspond to a method, aprogram, a procedure, a method of manufacturing or fabrication, etc. Oneembodiment may be described by a schematic drawing depicting a physicalstructure. It is understood that the schematic drawing illustrates thebasic concept and may not be scaled or depict the structure in exactproportions.

One disclosed feature of the embodiments is a technique for colorreflective or transmissive displays. The technique includes a stack ofcomponent blocks (e.g., cyan, magenta, yellow) color pixel architecture.Each component block includes a layer of colored fluid and an actuatorelement. The saturation of each color may be changed over its range bymodulating the thickness of the colored fluid underneath the actuatorelement such that the colored fluid is changed from a first state to asecond state. The two states are different in their volume geometry orstate. In one embodiment, the first state corresponds to a substantiallyplanar configuration, state, or geometry and the second statecorresponds to a substantially vertical configuration, state, orgeometry of the colored fluid volume, with respect to the substrate. Inanother embodiment, the first state corresponds to a substantiallyvertical configuration, state, or geometry and the second statecorresponds to a substantially planar configuration, state, or geometryof the colored fluid volume. The thickness of the colored fluid layermay be modulated by moving the actuator element with respect to thecolored fluid. The colored fluid is moved in response to the movement ofthe actuator element, thus changing its layer thickness, resulting invariable optical density. The variable optical density providescontrollable color contribution from each of the component colors in thecolor system. The actuation mechanism to move the actuator element maybe one of electric, magnetic, electrostatic, bimetallic, thermal,artificial muscles, electro-mechanical, chemo-mechanical, shape-memoryactuator, or any other suitable mechanism. The technique offers simplefabrication process and scalable large display size.

FIG. 1 is a diagram illustrating a display unit 100 in which oneembodiment may be practiced. The display unit 100 includes top andbottom substrates 110 and 120, and three component color blocks 130,140, and 150. The display unit 100 represents a reflective ortransmissive display of a pixel in color. A reflective display relies onthe ambient light for the display of the pixel. A transmissive displayuses a backlight to illuminate the pixel. The display unit 100 may beused in photography, printing, advertisement, signage, entertainment, orany other applications that need a versatile color display.

The top and bottom substrates 110 and 120 provide mechanical and opticalsealing for the stacked component color blocks 130, 140, and 150. Thetop substrate 110 receives light from an illuminating light sourcewhether from the ambient light or a back light illuminator. If the lightsource is the ambient light, then the light enters the top substrate110, goes through the color blocks 130, 140, and 150 and is reflectedback through these layers by the bottom substrate 120 or by a reflectorbelow the bottom substrate 120. If a back illuminator is used, then thelight from the back illuminator enters through the bottom substrate 120,goes through the color blocks 130, 140, and 150 and exits through thetop substrate 110. A color pixel 160 is formed as a result of theillumination of the component color blocks 130, 140, and 150 by thelight.

The three component color blocks 130, 140, and 150 are stacked on oneanother in a linear manner. Each of the blocks generates a componentcolor used in a color system. They are aligned to receive theilluminating light such that multiple component colors may be combinedor fused together to form the color of the resulting pixel 160.Depending on the amount of contribution of the component color in eachof the blocks, the resulting pixel may have a wide range of displaycolors. The color system used may be any convenient color system. In oneembodiment, the color system is the cyan, magenta, yellow (CMY) system.The resulting color is the result of the generally known subtractivecolor mixing mechanism. In a CMY display, which uses three blocks, arelatively wide color gamut may be achieved. However, more color blocksmay be added such as a black color block in order to achieve darkerblack states, similar to printing, or special custom colors. In somecases, one of the blocks may contain a color that is a specific companycolor, e.g., for advertisement purposes. Moreover, a display may includeonly one block, if color mixing is not required for the displayapplication. Other than the color, the structure and organization ofeach of the component color blocks 130, 140, and 150 are the same.Therefore, it is sufficient to describe one of the blocks. For brevity,in the following, the component color block 130 is used.

FIG. 2 is a diagram illustrating the component color block 130 shown inFIG. 1 according to one embodiment. The component color block 130includes a substrate layer 210, a layer of colored fluid 220, atransparent actuator element 230, and enclosure walls 240. It is notedthat the component color block 130 may include more or less than theabove components.

The substrate layer 210 provides mechanical and optical sealing andsupport for the block. For a transmissive display, it is transparent toallow optical transmission of light through the medium. For a reflectivedisplay, it may not be transparent and may be a reflective steel oraluminum foil, for example. If the block is the bottom block in theoptical unit 100, it may not be needed because the bottom substrate 120(FIG. 1) may be used. In that case the bottom substrate 120 may also bea simple reflector, such as a specular or diffuse reflecting surface.The layer 210 or substrate 120 may include a rigid material such asglass, but also a flexible material such as a polymer foil or sheet likeMylar™, plexiglass, polycarbonate, etc. The substrate may also includethin stainless steel if the display is only a reflective display.

The layer of colored fluid 220 is a layer of colored fluid in a cell onthe substrate layer 210. The colored fluid is a fluid dyed in a color,or the color may originate from a pigment or from nanoparticlesdispersed in a liquid as it is known that nanoparticle solutions maydisplay a color depending on the particle size. The color may be any ofthe component color in the color system (e.g., cyan, magenta, yellow).The colored fluid may be an ink. Colored inks may be prepared bydissolving a dye in a solvent, e.g. an aniline dye in water. A coloredfluid may also be obtained by dispersing pigments in a liquid medium,such as Hansa Yellow (Pigment Yellow 98) in ISOPAR provided by ExxonCorp. It typically has a low vapor pressure to prevent evaporation overtime. The dye may also include dichroic dyes for different color effectsin the reflected and transmitted mode. The colored fluid 220 may have awide range of viscosities. For example, it may have a low viscosity,similar to water (˜1 cP), which may allow fast switching speed. However,it may have a higher viscosity similar to glycerol (˜1500 cP) or honey(˜10,000 cP) or even higher for slower switching speed or increasedbistability of a color state. The colored fluid may also include aphase-change material such as a colored wax (e.g., candle wax orKemamide wax with dye or pigment). Such phase-change material may bebeneficial for a display with bistability as the material may have to beturned into a low-viscosity state before the actuator element 230 moves.Heating, with an integrated or external heater may cause such a phasetransition. In addition, irradiation with light such as UV or infraredlight may cause such a phase change. The portion of the layer of coloredfluid 220 directly under the element 230 has a thickness H. Since thecolored fluid 220 may be modulated or displaced, the thickness H may bevariable.

The transparent actuator element 230 is on the layer of the coloredfluid 220. It is transparent to allow illuminating light to go through.Typically, it is made of material that has an index of refraction thatis matched or close to the one of the colored or surrounding fluid toreduce refraction of light and reflection losses. The element 230 may beimmersed into the colored fluid 220. It may be moved, displaced, bent,or deformed in such a way that its immersion into the colored fluid 220modulates the thickness of the colored fluid 220, and in particular, thethickness H of the portion directly under the element 230. The movementof the element 230 may be activated by a force f. The force f may eitherpull or push the element 230 towards the substrate 210. The modulatedthickness of the colored fluid layer 220 provides a variable opticaldensity of the colored fluid layer 220. The variable optical density ofthe colored fluid layer 220 causes changes in the color contribution ofthe color component which means the lightness of the color is modulated.Accordingly, the lightness of the colored fluid layer 220 thatcontributes to the resulting pixel may be modulated or modified by themovement of the element 230. When this movement is activated orcontrolled by the force f, the actuation mechanism that generates theforce f acts as a control mechanism to control the generation of thecolor of the pixel. The variation of the optical density may be in thedirection of the applied force.

The transparent actuator element 230 may have a shape or size such thatit may be moved in an unrestricted manner within the block 130 and thethickness H of the portion of the colored fluid 220 directly beneath itcorresponds to color component of the pixel. In particular, it may bepositioned such that as it travels or as it is immersed into the coloredfluid 220, there is sufficient available space to allow unrestrictedmovement of the colored fluid 220 as the result of the immersion of theelement 230. As an example, assuming a square actuator element of1000×1000 microns and a 50 micron gap between element 230 and walls 240,a 3 micron thick layer of colored liquid may be displaced fromunderneath the actuator element 230 into the 50 micron wide space nextto the actuator element 230. The level of colored fluid layer 220 mayrise in this area from the initial 3 microns to ˜15-20 microns.Therefore, the actuator element 230 may have to be at least ˜20 micronshigh in this example. The space above the actuator element 230 may befilled with air or another gas or it may be occupied by a liquid,preferably a liquid that has a refractive index that matches thematerial of the actuator element 230.

The enclosure walls 240 may provide mechanical support and sealing forthe block. When the block 130 is well sealed, evaporation of the coloredfluid may be significantly reduced.

The block 130 may be in several states A, B, and C corresponding toseveral color lightness values or optical density values of the coloredfluid layer 220 as a result of the modulation of the thickness H. Thestates A, B, and C correspond to color component states 250A, 250B, and250C, shown in FIGS. 2A, 2B, and 2C, respectively. The first state, orstate A shows the state where the colored fluid 220 is in its originalstate, resulting in a full color contribution in the color componentstate 250A.

FIG. 2B is a diagram illustrating a component color block at a secondstate according to one embodiment. The second state, or state B,corresponds to the color component 250B. The state B is the state wherethe element 230 is moved or immersed into the colored fluid 220 suchthat the thickness H of the portion of the colored fluid under theelement 230 is reduced, resulting in less color contribution in thecolor component state 250B.

FIG. 2C is a diagram illustrating a component color block at a thirdstate according to one embodiment. The third state, or state C,corresponds to the color component 250C. The state C is the state wherethe element 230 is moved or immersed completely into the colored fluid220 such that the thickness H of the portion of the colored fluid underthe element 230 is reduced to zero, resulting in no color contributionin the color component state 250C.

FIG. 3 is a diagram illustrating the component color block 130 shown inFIG. 1 in three-dimensional space according to one embodiment. Forclarity, not all of the components are shown. The color block 130 isshown with two states, state A and state B. In state A, the actuatorelement 230 is in the upward position, resulting in a dark color. Instate B, the actuator element 230 is in a downward position where thethickness of the layer of colored fluid 220 is essentially zero,resulting in a light color, or no color contribution. The volume aboveor next to the actuator element 230 and above the colored fluid layer220 may be filled with air or a transparent fluid which does notintermix with the colored fluid. This transparent fluid may ideally havea refractive index that is matched to the material of the actuatorelement 230.

The color blocks like the block 130, 140, and 150 shown in FIG. 1 mayform a large display area including blocks positioned next to oneanother in a two-dimensional pattern. The shape of the individual blocksas seen from the top view may be any suitable geometrical shape. Someexamples are shown in FIGS. 4A, 4B, 4C, and 4D.

FIG. 4A is a diagram illustrating the top view of a square pattern ofthe adjacent color blocks according to one embodiment.

FIG. 4B is a diagram illustrating the top view of a rectangular patternof the adjacent color blocks according to one embodiment.

FIG. 4C is a diagram illustrating the top view of a hexagonal pattern ofthe adjacent color blocks according to one embodiment.

FIG. 4D is a diagram illustrating the top view of a triangular patternof the adjacent color blocks according to one embodiment.

The transparent actuator element 230 may be formed by a number of wayscorresponding to various embodiments of the invention.

FIG. 5A is a diagram illustrating the component color block 130 shown inFIG. 1 using a structure in a first state according to one embodiment.FIG. 5B is a diagram illustrating a component color block using astructure in a second state according to one embodiment. The transparentactuator element 230 may be a silicone, or polydimethylsiloxane (PDMS),structure that is suspended by a membrane 310. The actuator element 230may be also made of other organic or inorganic transparent materialssuch as glass, sapphire, plexiglass or Poly(methyl methacrylate) (PMMA),epoxy polymer, acrylates, polycarbonate, urethanes, or other transparentpolymers for example. The actuator element 230 may also include acombination of materials such as layers of several materials. In oneexample, the surface of the element 230 is coated with a fluoropolymeror with a silicone. The surface of element 230 or substrate 210 may alsobe roughened in order to prevent stiction between element 230 andsubstrate 210. Such roughening may be achieved by etching orsandblasting of the surface or by applying a rough surface coating suchas a micro- or nanoparticle based polymer layer. Small spacer bumps mayalso be patterned onto either surface, e.g. by inkjet printing or otherpattering methods. The actuator element 230 may be patterned byconventional machining, laser machining, molding, stamping,photolithography, etching, printing, etc. The membrane 510 may beflexible and attached to the enclosure walls 240 to restrict themovement of the element 230 within a predefined space or distance. Themembrane 510 may also be attached to the actuator element 230. It may beattached by bonding, laser-welding or it may be molded or otherwisepatterned from the same material as actuator element 230. The membrane510 may be substantially transparent and cover the surface of actuatorelement 230 or it may be only attached around the perimeter of actuatorelement 230 (in this case the membrane 510 may not have to betransparent). The membrane 510 may include a variety of materials, suchas Mylar, silicone, polycarbonate, PMMA, polyimide, epoxy polymer,fluorocarbon, metal, glass, etc. The thickness of the membrane is thinin order to allow movement of element 230 by applying only small forces.Typically, the membrane thickness may be 0.5 microns to 100 microns,depending on the geometry of the cell. In larger cells, extending overseveral millimeters or centimeters, the membrane may be made of thickermaterials, e.g., several hundred microns to millimeters thick. Themembrane may be attached to the side of wall 240 as shown in the figureor it may be attached to the top surface of wall 240, e.g., by a bondingmethod such as adhesive bonding, laser welding, ultrasonic bonding, etc.The membrane may be continuous or may be patterned into beam structuresin order to lower the spring constant. A wide range of beam structuresuspension geometries for mechanical elements such as micromirrors areknown in the art and are not described here in detail. One example ismeander-shaped beams between the walls 240 and the actuator element 230.The movement of the element 230 changes the colored fluid 220 from thefirst state, or state A where the fluid is in a substantially verticalposition to the second state, or state B where the fluid is in asubstantially planar position with respect to the substrate, or viceversa. In FIGS. 5A and 5B, the membrane 510 may provide the spring forcethat moves the element 230 back in contact with layer 210 when theexternal force f is removed. However, the geometry may also be in such away that the in the state of zero external force, there is a gap betweenthe element 230 and the substrate 210. In this case, the external forcepulls or pushes the element 230 towards the substrate and the springforce of the membrane may pull the element 230 away from the substrate210.

FIG. 6A is a diagram illustrating the component color block 130 shown inFIG. 1 using a perforated actuator element in a first state according toone embodiment. FIG. 6B is a diagram illustrating top view of thecomponent color block using a perforated actuator element in a firststate according to one embodiment. FIG. 6C is a diagram illustrating acomponent color block using a perforated actuator element in a secondstate according to one embodiment. FIG. 6D is a diagram illustrating topview of the component color block using a perforated actuator element ina second state according to one embodiment. The perforated actuatorelement provides additional vertical space for the colored fluid to moveinto a vertical position. The first state, or state A, is thetransparent state of the color block 130 and the second state, or stateB. is the opaque state. In the transparent state, the colored fluid ismoved into a substantially vertical position with regard to thesubstrate leaving a rather small cross-sectional viewing area for theviewer who looks at the color block 130 in a direction substantiallyperpendicular to the substrate.

FIG. 7A is a diagram illustrating the component color block 130 shown inFIG. 1 using a bimorph actuator in a first state according to oneembodiment. FIG. 7B is a diagram illustrating a component color blockusing a bimorph actuator in a second state according to one embodiment.

The transparent actuator element 230 may be a bimorph actuator, or otherbending actuator. The actuator may be realized by carbon nanotubesembedded in a polymer. This actuation mechanism in carbon nanotubes maybe based on expansion due to electrochemical double layer charging. Theactuator may be also a polymer gel actuator and the actuation may betriggered by light or electric signals. In one example the actuatorexpands due to the absorption of ions in an electric field. In aconventional bimorph actuator, the element 230 may include two materialssuch as a polymer (e.g. Mylar) and a transparent indium tin oxide layer,for example. When the materials are heated, e.g., by passing a currentthrough the conductive indium tin oxide layer, then the element 230 willbend due to the different thermal expansion of both materials. Whenactivated, the bimorph may be deformed or morphed into a shape such thatthe resulting thickness H of the portion of the colored fluid 220directly beneath the bimorph is non-uniform as shown in the first state,or state A. In the second state, or state B, the bimorph is flat andsubstantially in contact with the substrate. In this position, most ofthe colored fluid underneath the actuator is displaced to the sideswhere it assumes a substantially vertical position. The actuator element230 may be connected to an electrode and above the actuator, as well asabove the colored fluid layer 220, a transparent electrolyte may besituated. By applying a voltage between the actuator element 230 and theelectrolyte, ions or electrons move towards the or away from theactuator structure. This causes a deformation and is a generally knownmechanism in the art of electroactive polymers. The deformation may alsooriginate from other forces such as electrostatic forces, e.g., if avoltage between the substrate and the actuator causes a deformation ofthe actuator element 230. The element 230 may be attached to thesubstrate 210 for example in a center region, e.g., by spot welding. Itmay also be attached on one outer edge and in this case the elementwould curl up only from one side.

FIG. 8A is a diagram illustrating the component color block 130 shown inFIG. 1 using another actuation mode to move the colored fluid from asubstantially vertical into a substantially horizontal or planarposition in a first state according to one embodiment. FIG. 8A is adiagram illustrating the component color block 130 shown in FIG. 1 usinganother actuation mode to move the colored fluid from a substantiallyvertical into a substantially horizontal or planar position in a secondstate according to one embodiment. The transparent actuator element 230may be a polymer or glass actuation plate. The colored fluid 220 may bein a columnar configuration in the first state, or state A. Thesubstrate 210 may be coated at least partially by a low-surface energycoating 810 such as a fluorocarbon polymer (e.g., Cytop from Asahi Glassor Teflon AF from DuPont). The low-surface energy coating 810 may be acoating that has a water contact angle greater than 90 degrees. Theactuator element 230 may be similarly at least partially coated with alow surface energy coating. As the element 230 is activated to movedown, the colored fluid 220 may be spread out like a film in the secondstate, or state B. The colored fluid 220 may return to its originalcolumnar shape as the element 230 returns to its original position(state A). This is due to the requirement for conservation of volume andthe lateral position of the colored fluid column may be determined bythe low surface energy coating. In FIG. 8A, the low-surface energycoating is shown to cover the substrate surface, except for a centerregion where the fluid gets pinned (due to its higher surface energy).State A in FIG. 8A is a side view of the color block and the coloredfluid layer 220 is shown in the vertical position. In this verticalposition the fluid may have the shape of a circular column (circularshape as seen from top) or it may have the shape of a long wall(elongated rectangular stripe shape as seen from top). In both of theseconfigurations of state A, the color block 130 appears substantiallytransparent when viewed from a direction substantially perpendicular tothe substrate because the fluid column occupies only a small percentageof the total surface area of the color block. For example, assume thatin state B the colored fluid layer 220 has the shape of a square disk ofdimension 1000×1000×3 micrometers and in state A this layer has theshape of a wall of 1000×100×30 micrometers. In this case, the actuatorelement 230 moves from a height of 3 microns above the substrate (stateB) to a height of 30 microns above the substrate (state A). The coloredfluid layer 220 in FIG. 3D forms a wall-like column extending into theplane of the illustrated side-view. Both fluid volumes are the same, butwhile in state B the colored fluid layer 220 covers all of the cell areaof the color block, in state A it only occupies 10 percent of the area.The color block therefore appears much more transparent to the viewer.Thin spacers on the substrate or on the actuator element 230 may serveto define the lower position (e.g., the 3 micron gap in the aboveexample). Those spacers may be deposited (e.g., by inkjet printing) orthey may be otherwise patterned into or onto the substrate or theactuator element.

FIG. 9A is a diagram illustrating the component color block 130 shown inFIG. 1 using an electrostatic force in a first state according to oneembodiment. FIG. 9B is a diagram illustrating the component color block130 shown in FIG. 1 using an electrostatic force in a second stateaccording to one embodiment. The transparent actuator element 230 may beany of the structures described above. The block 130 includes a sealsubstrate 910 which may be the substrate layer of the upper block. Thislayer 910 may be a thin glass plate that is at least partially coatedwith a transparent conductor such as indium tin oxide, zinc oxide,Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), orit may be coated with narrow patterned lines of a non-transparentconductor such as chromium or aluminum. A membrane 920 is attached tothe element 230. The membrane 920 may include a thin polymer foil madeof materials such as Polyethylene terephthalate (PET), e.g., Mylar,polyethylene naphthalate (PEN), PDMS, Saran, epoxy, fluorocarbon, etc.The foil may carry a permanent charge such as in the case of an electretor it may be coated with a transparent conductor or it may be patternedwith narrow lines of a non-transparent conductor. The membrane 920 mayalso have conducting elements, such as a network of conducting carbonnanotubes, embedded in its polymer matrix. The membrane 920 and thesubstrate 910 are connected to a voltage source. At the first state, orstate A, there is no voltage applied and there is no electrostaticforce. The element 230 is at its original position. As a voltage V 930is applied, an electrostatic force f is generated and moves the element230 up to change to the second state, or state B. If the membrane 920carries a permanent charge such as in an electret, the voltage may beapplied between a conductive layer on the substrate 210 and the sealsubstrate 910 to generate an electric field in which the membrane 920may be deflected. As described earlier, the membrane may be patternedinto beam-shaped suspension structures, such as straight, curved ormeandering beams between element 230 and walls 240 to adjust the springconstant. A very similar configuration as shown in FIG. 9A and FIG. 9Bmay be employed in a magnetic actuation scheme. Here, the actuatorelement 230 or the suspension membrane 920 may contain ferromagneticelements, such as ferromagnetic nanoparticles, patterned traces offerromagnetic material such as nickel, magnetite, cobalt, etc. These mayhave been patterned or deposited by commonly known patterning methodssuch as printing, etching, laser ablation, evaporation, etc. In oneexample, magnetite nanoparticles are inkjet printed in a sparse patternonto the top surface of actuator element 230 or suspension membrane 920.In another example, nickel traces or nickel dots are evaporated onto thesurface of element 230 via a shadow mask. A coil structure which ispatterned on the surface of substrate 910 generates a magnetic fieldwhich attracts the actuator element 230 when a current is passed throughit. The coil may be made form a patterned layer of transparent indiumtin oxide or of another patterned conducting material. Of course, theferromagnetic element may also be attached to the substrate 910 and themagnetic field generating conducting traces may be patterned onto theactuator element 230 or suspension membrane 920.

FIG. 10A is a diagram illustrating the component color block 130 shownin FIG. 1 using an electro-active polymer (EAP) in a first stateaccording to one embodiment. FIG. 10B is a diagram illustrating thecomponent color block 130 shown in FIG. 1 using an electro-activepolymer (EAP) in a second state according to one embodiment. A sealsubstrate 1010 may be attached to the walls 240 to form a chamber. Thetransparent actuator element 230 may be any of the structures describedabove. It may be suspended by a membrane 1020. Its movement may beactuated by an electro-active polymer (EAP) 1030. An example of anelectroactive polymer is reversibly redox tunable, swellable andshrinkable metallopolymer gels such as a weakly cross-linkedpolyferrocenylsilane. The block 130 includes an electrode 1040 and anelectrolyte 1050 to provide electrical activation for the EAP 360. Theelectrolyte 1050 may be a transparent ionic fluid that fills thechamber. The EAP 1030 may be positioned between the substrate layer 210and the actuator element 230. The EAP 1030 may expand or contract tomove the transparent actuator element 230 when a voltage is applied tothe electrode that causes ion diffusion through the electrolyte 1050. InFIG. 10A, the EAP 1030 expands in the first state, or state A, to pushthe element 230 upward. In FIG. 10B, the EAP 1030 contracts in thesecond state, or state B, to move the element 230 down. Variouselectroactive polymer materials are possible, including polymer gels orstacks of piezoelectric polymers (piezoelectric polymers do not requirethe surrounding electrolyte and the electrolyte 1050 may be replaced byan index-matching fluid). An example of piezoelectric polymers isPolyvinylidene Fluoride (PVDF) or PVDF-trifluoroethylene (TrEF)copolymer. The structure in FIGS. 10A and 10B may also contain reservoirregions or the membrane 920 may contain holes to compensate for volumechanges. Other electrically actuated gels and artificial muscleactuators may be employed. Example materials are polyacrylic acidpolyvinylalcohol gels or polyvinylalcohol gels swollen withdimethylsulfoxide. These gels may either bend or swell in an electricfield.

FIG. 11A is a diagram illustrating the component color block 130 shownin FIG. 1 using a shape memory actuator in a first state according toone embodiment. FIG. 11B is a diagram illustrating the component colorblock 130 shown in FIG. 1 using a shape memory actuator in a secondstate according to one embodiment. The transparent actuator element 230may be any of the structures described above. The transparent actuatorelement 230 may be attached to a membrane 1110. The actuation mechanismfor the actuator element 230 may be provided by a shape-memory actuator1130. The top of the element 230 may be cam head 1120 that is shaped tofit the shape-memory actuator 1130 such that a horizontal movement ofthe shape-memory actuator 1130 causes a vertical movement of theactuator element 230. In FIG. 11A, the shape-memory actuator 1120 is atan original position and the element 230 and the fluid layer 220 are inthe first state, or state A. In FIG. 11B, the shape-memory actuator 1120moves horizontally pushing the element 230 downward in the second state,or state B. The membrane 1110 may provide the suspension for theactuator element 230 and it may also provide the spring-force that movesthe element 230 into the up position. The shape memory actuator 1130provides the force to bend the membrane 1110 and the element 230downwards. However, the element 230 may also be directly coupled to theshape memory actuator 1130 so that the actuator 1130 provides the forcefor up and down movement.

FIG. 12A is a diagram illustrating a top view of the shape memoryactuator 1130 shown in FIGS. 11A and 11B according to one embodiment.FIG. 12B is a diagram illustrating a side view of the shape memoryactuator 1130 shown in FIGS. 11A and 11B according to one embodiment.The shape-memory actuator 1130 includes a cam structure 1210 and a wireassembly. The wire assembly may include wires 1220 and 1230. The camstructure 1210 may be shaped to fit the cam head 1120 of the element 230when in state A where the element 230 is in an upward position. The twowires 1220 and 1230 are loops around the cam structure 1210 and attachedto two sides of the enclosure walls 240. The wire 1220 and 1230 may bethermally activated by electric current. TiNi (NiTinol) is a typicalshape memory compound and wire made of this material is commerciallyavailable. As current passes through the wires, heat is generatedcausing the wires to contract due to the shape memory effect. As currentis reduced or turned off, the wires are cooled down and expand. Theexpansion and contraction of the shape-memory wires 1220 and 1230 causethe cam structure 1210 to move, or shuttle, horizontally back and forth.At state B, the cam structure 1210 is moved such that it pushes theactuator element 230 down. In other words, the wire assembly of thewires 1220 and 1230 causes a horizontal movement of the cam structure1210 when an electrical current is applied. The horizontal movement ofthe cam structure 1210 causes a vertical movement of the actuatorelement 230. It is noted that the arrangement and design of the shapememory actuator 1130 shown in FIGS. 11A, 11B, 12A and 12B are merely forillustrative purposes.

FIG. 13A is a diagram illustrating the component color block 130 shownin FIG. 1 using a bi-stable display operation in a first state accordingto one embodiment. FIG. 13B is a diagram illustrating the componentcolor block 130 shown in FIG. 1 using a bi-stable display operation in asecond state according to one embodiment. Bi-stability may be used in adisplay for low power consumption. Some actuation mechanisms, such aselectrostatic actuation, do not provide bi-stability unless used in alatching design. The transparent actuator element 230 may be any of thestructures described above. The movement of the colored fluid 220 mayhave to overcome an energy barrier caused by a low surface energybarrier 1310. The low surface energy barrier 1310 may cause a bistablestate of the actuator element 230. It may be formed by a hydrophobicmaterial arranged along the edges of the actuator element 230. Suchmaterial may be a fluorocarbon polymer such as Teflon (DuPont) or Cytop(Asahi Glass) or Parylene. The energy barrier is generated in thisembodiment by the requirement of the fluid to move past the hydrophobicstructure in order to change from the first state, or state A, shown inFIG. 13A, to the second state, or state B, shown in FIG. 13B. Thecolored fluid 220 may be chosen so that its movement is repelled, orinhibited, by the hydrophobic barrier. In one example, the dyed orcolored fluid 220 is water based and the low-surface energy barrier 1310is made of Teflon. The low-surface energy barrier 1310 may be patternedby photolithography and etching, by ink-jet printing, by shadow-maskevaporation. Although the low surface energy barrier is only illustratedas part of element 230, it may also or additionally be patterned on thesubstrate 210 or walls 240 in FIGS. 2A, 2B, and 2C.

The actuation mechanism of the transparent actuator element 230 maycause a force to move the transparent actuator element 230. The forcemay be caused by one of a mechanical force, a bimetallic actuation, athermal actuation, an electric field, a magnetic field, anelectro-magnetic field, an electrostatic force, a deformation of anelectroactive polymer or a deformable polymer, and a shape-memoryactuator. The addressing scheme for all the described displays may bebased on active matrix addressing in which active matrix pixel circuitsare patterned and connected to the color elements. The pixels mayprovide a current or an electric potential in order to address theindividual color elements.

A dynamic actuation mechanism may rely on viscosity differences betweenCMY inks. Similar driving mechanisms have been proposed by E-ink forcolor electrophoretic displays in which the mobility of particles isdifferent for each color. A pulse generator may be used to generate asuitable pulse. A short pulse (of the actuation force) may deflect astructure with low viscosity ink but not the one with high viscosityink. A long pulse may deflect a structure with high viscosity ink but italso deflects the one with low viscosity ink. However, the structurewith low-viscosity ink returns faster to its un-deflected state. Byselecting and appropriate sequence of short and long pulses, severalcolor states can be achieved in a stack of color cells. In this drivingscheme the force, electric field or other mechanical force, may beapplied across all the stacked cells.

The actuation of individual cells may also occur by providing anelectrode to each individual cell. This may require vertical vias toeach layer. For larger display cells, other actuation schemes may beapplied. For example, a microphone membrane may be used to deflect apatterned polydimethylsiloxane (PDMS) membrane.

FIG. 14A is a diagram illustrating a component color block 130 shown inFIG. 1 using an electroactive polymer in a first state according to oneembodiment. FIG. 14B is a diagram illustrating a component color block130 shown in FIG. 1 using an electroactive polymer in a second stateaccording to one embodiment. A transparent electrode 1420 may beattached to a seal substrate 1410. Electrodes 1430 may be attached tothe enclosure walls 240, but other electrode configurations arepossible. An electrolyte 1440 may be provided between the electrodes1420 and 1430. An electrolyte is a substance containing free ions and anexample may be ammonium chlorite NaClO₄. Also solid polymer electrolytessuch as polyacrylonitrile plasticised with propylene carbonate andethylene carbonate containing 1.0 M NaClO₄ may be used in conjunctionwith electroactive polymers. The colored fluid 220 may be an oil thatdoes not mix with the electrolyte 1440. The actuator element 230 is anelectroactive polymer (EAP) that may have volume change upon activatedby an electrical voltage. Conducting polymers such as polypyrrole (PPy)and poly-3,4-ethylenedioxythiophene (PEDOT) may undergo volumetricchanges as they are oxidized or reduced. When a voltage is applied toelectrodes the electrodes 1420 and 1430, the actuator element 230 isexpanded. The expansion of an ionic electroactive polymer is based onthe transfer and diffusion of ions throughout the polymer. In oneexample the expansion is due to by ion (e.g., chlorate ion) and waterabsorption. When the voltage is removed or reversed, the actuatorelement 230 contracts and resumes its original shape. The volume changemay also be caused by a reversibly redox tunable swellable-shrinkablemetallopolymer gel such as polyferrocenylsilane.

FIG. 15 is a diagram illustrating a pixel addressing using localizedcharges according to one embodiment. FIG. 15A is a diagram illustratinglocalized charges according to one embodiment. The address scheme may beillustrated by two elements 1510 and 1520, but it may be extended tomore than two elements.

The two elements 1510 and 1520 correspond to the transparent actuatorelements in the stacked blocks as shown in FIGS. 1 and 2. The elements1510 and 1520 may extend over several pixels. In this example, two pixelelectrodes 1530 and 1540 are shown. A counter-electrode 1550 is shown.Each of the elements 1510 and 1520 may be locally charged by electriccharge or magnetic particles. The pixel electrode directly underneaththe region that is locally charged causes a force to move the element. Avoltage between the pixel electrode and the counter plate at the topgenerates an electric field in which the charge moves. In the case ofmagnetic particles, the particles move in a magnetic field gradient. InFIG. 15A, the negative counter-ions are in the surrounding fluid and thecancel the charges on the actuator element 1510. When a field isapplied, the positively charged actuator element 1510 and the negativecounter charges move in opposite directions.

The charge or localized magnetic property may be attached to the elementby any suitable technique such as by a printing process. A chargingcompound (e.g., a silane or other commonly known compound) or chargedirector (e.g. a metal salt) commonly used in the art of electrophoretictoner may be added to the polymer. The polymer may also be locallycharged by e-beam writing to form an electret. In the case of electriccharge, the pixel electrodes may be capacitor plates and an electricfield may be established between the pixel electrode and an opposingcounter-plate which may be held at a ground potential. In a dielectricliquid, the elements 1510 and 1520 may be porous, e.g., containingholes, in the region of the charge so that the counter charge may bestripped off when the element is moving. The charge may be localized inthe material on the surface. Negative charge may cause the element tomove up and positive charge may cause the element to move down.

In case of magnetic actuation, the magnetic particles may be embeddednano-particles (e.g., iron oxide, nickel) by suitable process (e.g.,inkjet printing) or micro-magnets (e.g., NdFeB) for larger pixel sizes.Each pixel may include a small coil with an optional ferrite core.Magnetic addressing may be suitable for large pixel displays.

FIG. 16 is a flowchart illustrating a process 1600 to construct adisplay unit according to one embodiment.

Upon START, the process 1600 deposits a layer of colored fluid on asubstrate layer (Block 1610). The layer of colored fluid has a thicknessand a color. Then, the process 1600 forms a transparent actuator elementon the layer of the colored fluid (Block 1620). Next, the process 1600forms an actuation mechanism to create a force causing movement of thetransparent actuator element when activated (Block 1630). The movementof the transparent actuator element modulates the thickness of the layerof colored fluid that is underneath the actuator element. The modulatedthickness provides a variable optical density of the colored fluid. Theprocess 1600 is then terminated.

FIG. 17 is a flowchart illustrating the process 1620 shown in FIG. 16 toform an actuator element according to one embodiment.

Upon START, the process 1620 forms one of a silicone structure attachedto a suspension membrane, a perforated actuator element, an expandingpolymer, a bimorph actuator, and an electro-active polymer. The process1620 is then terminated.

FIG. 18 is a flowchart illustrating the process 1630 shown in FIG. 16 toform an actuation mechanism according to one embodiment.

Upon START, the process 1630 determines the type of mechanism (Block1810). If it is an electric or magnetic mechanism, the process 1630 addselectric charge or magnetic particles into the transparent actuatorelement (Block 1820) and is then terminated. If the type of mechanism isan electrostatic mechanism, the process 1630 forms an electrostaticgenerator (Block 1830). Then, the process 1630 adds transparent ionicfluid to the layer of colored fluid (Block 1840) and is then terminated.If the type of mechanism is based on viscosity, the process 1630 forms apulse generator to generate a pulse that causes deflection of theactuator element based on the viscosity of the colored fluid (Block1850). The process 1630 is then terminated. If the type of mechanism isa shape memory actuator, the process 1630 forms a shape memory actuatorcomprising a cam structure shuttled by thermal wires (Block 1860) and isthen terminated. The thermally induced horizontal movement of the camstructure causes a vertical movement of the actuator element. If thetype of mechanism is a bi-stable display operation, the process 1630forms a low surface energy barrier (e.g., hydrophobic barrier) along theedges of the actuator element (Block 1870) and is then terminated. Ifthe type of mechanism is deformable polymer, the process 1630 forms anelectrode or electrodes and electrolyte to expand or contract theelectroactive polymer (EAP) (Block 1880). The EAP may be the actuatorelement itself or may be used to move the actuator element. The process1630 is then terminated.

All or part of an embodiment may be implemented by various meansdepending on applications according to particular features, functions.These means may include any one of mechanical, solid, liquid, optical,sonic, electro-mechanical, electro-optical, electric, magneticcomponents, or any combination thereof.

It will be appreciated that various of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Variouspresently unforeseen or unanticipated alternatives, modifications,variations, or improvements therein may be subsequently made by thoseskilled in the art which are also intended to be encompassed by thefollowing claims.

What is claimed is:
 1. An apparatus comprising: a substrate layer; alayer of colored fluid on the substrate layer, the layer of coloredfluid having a thickness and a color; and a transparent actuator elementon the layer of the colored fluid to modulate the thickness of thecolored fluid upon being activated by a force such that the coloredfluid is changed from a first state to a second state or vice versa, themodulated thickness providing a variable optical density of the coloredfluid, wherein the transparent actuator element comprises one of astructure attached to a suspension membrane, a perforated element, anexpanding polymer, a bimorph actuator, and an electro-active polymer;and a low-surface energy barrier arranged along edges of the actuatorelement, the low-surface energy barrier causing a bistable state of theactuator element.
 2. The apparatus of claim 1 wherein the transparentactuator element comprises one of a structure attached to a suspensionmembrane, a perforated element, an expanding polymer, a bimorphactuator, and an electro-active polymer.
 3. The apparatus of claim 1wherein the bimorph actuator comprises one of: carbon nanotubes embeddedin a polymer; a polymer gel actuation triggered by light or anelectrical signal; and a polymer and a transparent oxide layer.
 4. Theapparatus of claim 1 wherein the force is caused by one of a mechanicalforce, a bimetallic actuation, a thermal actuation, an electric field, amagnetic field, an electro-magnetic field, an electrostatic force, and adeformation of an electroactive polymer.
 5. The apparatus of claim 1wherein the color is one of cyan, magenta, yellow, and black.
 6. Theapparatus of claim 1 wherein the colored fluid has a viscosity rangingfrom approximately 1 cP to approximately 10,000 cP.
 7. An apparatuscomprising: a substrate layer; a layer of colored fluid on the substratelayer, the layer of colored fluid having a thickness and a color; and atransparent actuator element on the layer of the colored fluid tomodulate the thickness of the colored fluid upon being activated by aforce such that the colored fluid is changed from a first state to asecond state or vice versa, the modulated thickness providing a variableoptical density of the colored fluid, wherein the transparent actuatorelement comprises one of a structure attached to a suspension membrane,a perforated element, an expanding polymer, a bimorph actuator, and anelectro-active polymer; a seal substrate and walls to enclose theactuator element and the colored fluid in a chamber; and an electrolytefilling the chamber.
 8. The apparatus of claim 7 further comprising: anelectrode attached to the substrate layer; and an electroactive polymer(EAP) positioned between the electrode and the actuator element to movethe actuator element when a voltage applied to the electrode to causethe EAP contract or expand by ion diffusion through the electrolyte. 9.The apparatus of claim 7 further comprising: electrodes attached to theseal substrate and the walls to cause the actuator element being theelectroactive polymer to contract or expand by ion diffusion through theelectrolyte when a voltage is applied.
 10. A method comprising: stackinga plurality of layers of colored fluid on each other, each of thecolored fluid having a color and a thickness and being on a substratelayer; and activating a force on a transparent actuator element on eachof the layers of the colored fluid to modulate the thickness such thatthe colored fluid is changed from a first state to a second state orvice versa, the modulated thickness providing a variable optical densityof the colored fluid.
 11. The method of claim 10 wherein the transparentactuator element comprises one of a structure attached to a suspensionmembrane, a perforated element, an expanding polymer, a bimorphactuator, and an electro-active polymer.
 12. The method of claim 10wherein activating the force comprises: applying the force being one ofa mechanical force, a bimetallic actuation, a thermal actuation, anelectric field, a magnetic field, an electro-magnetic field, anelectrostatic force, and a deformation of an electroactive polymer. 13.The method of claim 10 wherein the colored fluid has a columnar shapesuch that the colored fluid is spread out in the first state as theactuator element moves down and returns to the columnar shape in thesecond state as the actuator element moves up.
 14. A method comprising:stacking a plurality of layers of colored fluid on each other, each ofthe colored fluid having a color and a thickness and being on asubstrate layer; activating a force on a transparent actuator element oneach of the layers of the colored fluid to modulate the thickness suchthat the colored fluid is changed from a first state to a second stateor vice versa, the modulated thickness providing a variable opticaldensity of the colored fluid; and arranging a low-surface energy barrieralong edges of the actuator element, the low-surface energy barriercausing a bistable state of the actuator element.
 15. A methodcomprising: stacking a plurality of layers of colored fluid on eachother, each of the colored fluid having a color and a thickness andbeing on a substrate layer; activating a force on a transparent actuatorelement on each of the layers of the colored fluid to modulate thethickness such that the colored fluid is changed from a first state to asecond state or vice versa, the modulated thickness providing a variableoptical density of the colored fluid; and generating a sequence ofpulses of appropriate lengths to deflect the colored fluid in each ofthe layers based on viscosity of the colored fluid, the deflectedcolored fluid returning to an undeflected state according to theviscosity.
 16. A method comprising: stacking a plurality of layers ofcolored fluid on each other, each of the colored fluid having a colorand a thickness and being on a substrate layer; activating a force on atransparent actuator element on each of the layers of the colored fluidto modulate the thickness such that the colored fluid is changed from afirst state to a second state or vice versa, the modulated thicknessproviding a variable optical density of the colored fluid, whereinactivating the force comprises: applying the force being one of amechanical force, a bimetallic actuation, a thermal actuation, anelectric field, a magnetic field, an electro-magnetic field, anelectrostatic force, and a deformation of an electroactive polymer,wherein applying the force comprises: applying a voltage to an electrodeto cause ion diffusion through an electrolyte that causes contraction orexpansion of the electroactive polymer positioned between the actuatorelement and the substrate layer.
 17. A method comprising: stacking aplurality of layers of colored fluid on each other, each of the coloredfluid having a color and a thickness and being on a substrate layer;activating a force on a transparent actuator element on each of thelayers of the colored fluid to modulate the thickness such that thecolored fluid is changed from a first state to a second state or viceversa, the modulated thickness providing a variable optical density ofthe colored fluid, wherein activating the force comprises: applying theforce being one of a mechanical force, a bimetallic actuation, a thermalactuation, an electric field, a magnetic field, an electro-magneticfield, an electrostatic force, and a deformation of an electroactivepolymer, wherein applying the force comprises: applying a voltage toelectrodes to cause ion diffusion through an electrolyte that causescontraction or expansion of the electroactive polymer or an expandingpolymer being the actuator element.